1. Field
The presently disclosed subject matter relates to a vehicle headlight including a projector headlight using LED optical units for a low beam, and more particularly to a vehicle headlight including a projector headlight for a low beam having a favorable light distribution pattern and a high visual/visible quality.
2. Description of the Related Art
Recently, various vehicle headlights using LED optical units have been developed. This development has been brought about because LEDs have a long life and are battery friendly as compared with a light bulb, discharge lamp, etc. On the other hand, because it is difficult to conform to a light distribution standard for a headlight using one LED chip, vehicle headlights using a plurality of LED optical units have been developed.
A first conventional headlight shown in FIG. 11 is a projector headlight that is disclosed in patent document No. 1 (Japanese Patent Application Laid Open JP2006-172829). The projector headlight is provided with a plurality of projector type optical units 60-63 having a respective optical axis Z60-Z63. Each of the optical units 60-63 can form substantially a same light distribution pattern with respect to each of the optical axes Z60-Z63. A first optical unit 60 is attached to a vehicle so that the optical axis Z60 thereof is located in parallel with a central line of the vehicle. A second optical unit 61 is attached to the vehicle so that the optical axis Z61 thereof intersects with the optical axis Z60 of the first optical unit 60 at a first angle in front of the vehicle. Similarly, third and forth optical units 62, 63 are attached to the vehicle so that their respective optical axes Z62, Z63 intersect with the optical axis Z60 of the first optical unit 60 at a second angle and a third angle, respectively.
In this case, the optical units 60-63 are attached on a circular arc so that the above-described intersection angles become larger in order of the first, second and third angles. Therefore, the projector headlight can be arranged in a small space, and also can emit light along a road including a curved road by controlling light(s) emitted from the optical units 60-63. However, variability in brightness may be caused on a middle portion between the light distribution patterns formed by adjacent optical units. In order to prevent this variability in brightness, it may be necessary to increase the number of the optical units in the first conventional headlight.
In order to provide a favorable light distribution while preventing an increase in the number of the optical units, a second conventional headlight shown in FIG. 12 is disclosed in patent document No. 2 (Japanese Patent Application Laid Open JP2007-5182). The second headlight includes a plurality of projector type optical units 70-74 and a bracket 75 that can rotatably connect the optical units 70-74. Accordingly, the headlight may be applicable to an Adaptive Front-lighting System (AFS), which can change a light-emitting direction and a light distribution pattern according to a travelling circumstance of a vehicle.
However, it is difficult for the above-described conventional headlights to form an elbow line and various cutoff lines for a low beam in their light distribution patterns. With regard to the first conventional headlight, this is because the light distribution pattern among optical units 60-63 is substantially the same. In the second conventional headlight, it may be because each of light distribution patterns formed by the optical units 70-74 changes according to various circumstances.
Patent document No. 3 (Japanese Patent Application Laid Open JP2005-294176) discloses a third conventional headlight that may form various cutoff lines such as a horizontal cutoff line, an elbow line, etc. The third conventional headlight shown in FIG. 13 includes a plurality of optical units 82-86 that are provided with a light-emitting semiconductor device 81 and a reflector for reflecting light emitted from the light-emitting semiconductor device 81. In addition, the headlight includes a cylindrical lens 87 that is located in front of the optical units 82-86 so as to extend along the optical units 82-86 that are located in a horizontal direction.
In this case, first and second optical units 82-83 are located so that both optical axes thereof expand at a predetermined angle in a direction toward light-emission of the headlight and in a horizontal direction. Therefore, these optical units 82-83 can form a light distribution pattern that expands in a direction from an incoming lane toward the outside of a driving lane via the cylindrical lens 87. Other optical units 84-86 can form a light distribution pattern including the horizontal cutoff line and the elbow line via the cylindrical lens 87.
However, in order to form the light distribution pattern it may be necessary to control the light emitted from each of the plurality of optical units 82-86 using the cylindrical lens 87 that is formed as one long lens. Therefore, to form a favorable light distribution pattern, it may be necessary to prepare the above-described optical parts with high accuracy for the third conventional headlight and to adjust the locations of these optical parts.
A fourth conventional headlight including a plurality of optical units that can form a respective individual light distribution pattern is disclosed in patent document No. 4 (Japanese Patent Application Laid Open JP2005-141919). As shown in FIG. 14, the fourth conventional headlight includes a plurality of projector type optical units 90-93 that are located in a horizontal direction and a plurality of reflector type optical units 94-95 that are located under the optical units 91-93. In FIG. 14, only the optical unit 90 is shown. The other optical units 91-93 are not shown in order to show the optical units 94-95.
The optical units 90-93 can form a light distribution pattern including a hot zone, a horizontal cutoff line and an elbow line by combining light emitted from each of the projector type optical units 90-93. The reflector type optical units 94-95 can form a light distribution pattern that expands in a direction from an incoming lane toward the outside of a driving lane under the horizontal cutoff line. Therefore, because each of the optical units 90-95 can form an individual light distribution pattern without light interception, light use efficiency may be improved.
In addition, the fourth conventional headlight may form a favorable light distribution pattern using the combined light emitted from the optical units 90-95. However, the headlight may cause a problem such that power consumption may increase due to the many optical units. Therefore, patent document No. 5 (Japanese Patent Application Laid Open JP2008-13014) discloses a fifth conventional headlight as shown in FIG. 15.
The headlight includes a plurality of projector optical units 50-52 that can form a light distribution pattern including the hot zone, the horizontal line and the elbow line by combining light emitted from each of the optical units 50-52. The headlight also includes a reflector type optical unit 53 which can form a light distribution pattern that expands in a direction from an incoming lane toward the outside of a driving lane under the horizontal cutoff line. In this case, by controlling each amount of light emitted from the optical units 50-53, the headlight may improve visibility on the light distribution pattern while preventing increase of power consumption.
However, the fifth conventional headlight may cause a problem in that the driver circuit may become complex. In addition, the fourth and the fifth conventional headlights are constructed from the projector type optical units and the reflector type optical units, that is, by two different type units. Therefore, the structure may decrease the possible range of headlight design, and also may cause an unspectacular outside appearance.
The above-referenced Patent Documents are listed below and are hereby incorporated with their English abstracts in their entireties.    1. Patent document No. 1: Japanese Patent Application Laid Open JP2006-172829    2. Patent document No. 2: Japanese Patent Application Laid Open JP2007-5182    3. Patent document No. 3: Japanese Patent Application Laid Open JP2005-294176    4. Patent document No. 4: Japanese Patent Application Laid Open JP2005-141919    5. Patent document No. 5: Japanese Patent Application Laid Open JP2008-13014
The disclosed subject matter has been devised to consider the above and other problems, characteristics and features. Thus, an embodiment of the disclosed subject matter can include a vehicle lamp including a projector headlight using projector type optical units for a low beam that can provide a favorable light distribution pattern including a cutoff line and an elbow line with a simple driver circuit. In this case, the projector headlight for a low beam can be constructed only from the projector type optical units that can be formed substantially in a same thin shape. Thus, the projector headlight can result in an increase in the possible range of headlight design and in a high visual quality.